Linear alkylbenzene sulfonate (LAS) promotes sedimentation and lipid accumulation in Scenedesmus obliquus

Abstract

The lipids found in microalgae are promising raw materials for bio-diesel production. This study tests the effects of linear alkylbenzene sulfonate (LAS) on the growth, colony formation, sedimentation and lipid content of the green alga Scenedesmus obliquus. Growth of S. obliquus was unaffected by LAS below concentrations of 100 mg L⁻¹. LAS treatment promoted colony formation and the number of cells per aggregate significantly increased with rising LAS concentration. Both optic and scanning electron microphotoes showed that the induced colony of S. obliquus was regular and there were clear attachment points between two neighboring cells. The sedimentation efficiency at 10 min significantly increased with the increasing LAS concentration. Under treatment of 100 mg L⁻¹ LAS, the sedimentation efficiency was 69.0% after 40 minutes' settling, which was 30% higher than that in the control group. The sedimentation efficiency was positively related to cells per colony at all sedimentation time except for 60 min. Moreover, the lipid content was 21.2% when treated with 100 mg L⁻¹ LAS, which was 1.18 times higher than in the control group. The main fatty acid composition of S. obliquus was α-linolenic acid (C18:3) and palmitic acid (C16:0). The degree of fatty acid unsaturation was not obviously affected by LAS addition but the proportion of fatty acid with the chain length ranging from C16 to C18 was promoted from 70.9% to 84.2% by LAS addition. This result indicated that LAS addition was beneficial to improve the quality of algal biodiesel. Our results suggested that moderate doses of LAS can effectively enhance the sedimentation efficiency of S. obliquus by inducing colony formation and improving the lipid content of the cells without inhibiting their growth.